Current industrial automotive trends to reduce the number of overall mechanical components of the vehicle and to reduce the overall vehicle weight have contributed to the development of system-by-wire applications, typically referred to as X-by-wire systems. One such X-by-wire system that has recently received increased attention is a brake-by-wire (BBW) system, sometimes referred to as an electronic braking system (EBS).
Unlike conventional mechanical braking systems, BBW systems actuate one or more vehicle braking components via an electric signal that is generated by an on-board processor/controller. BBW systems typically remove any direct mechanical linkages and/or hydraulic force-transmitting-paths between the vehicle operator and the brake control units. In some systems, a BBW system supplants a conventional hydraulic fluid-based service braking system with an electrical-based system to perform basic braking functions.
Various design techniques have been implemented to promote the reliability of the BBW system including, for example, redundancy, fault tolerance to undesired events (e.g., events affecting control signals, data, hardware, software or other elements of such systems), fault monitoring, and fault recovery. One design approach to provide fault tolerance which has been utilized in BBW control systems has been to include a mechanical backup system which is separate from the BBW system and operates as an alternate means for braking the vehicle. These systems, however, add undesirable weight and packaging complexity to the vehicle.